[gcc/devel/c++-modules] Fix incorrect filling of delay slots in branchy code at -O2

[gcc/devel/c++-modules] Fix incorrect filling of delay slots in branchy code at -O2

[Nathan Sidwell]

https://gcc.gnu.org/g:3e6ab5cefa81165e90fb62abf50e515f85a17e9a

commit 3e6ab5cefa81165e90fb62abf50e515f85a17e9a
Author: Eric Botcazou <ebotcazou@gcc.gnu.org>
Date:   Fri Mar 13 09:58:44 2020 +0100

    Fix incorrect filling of delay slots in branchy code at -O2
    
    The issue is that relax_delay_slots can streamline the CFG in some cases,
    in particular remove BARRIERs, but removing BARRIERs changes the way the
    instructions are associated with (basic) blocks by the liveness analysis
    code in resource.c (find_basic_block) and thus can cause entries in the
    cache maintained by resource.c to become outdated, thus producing wrong
    answers downstream.
    
    The fix is to invalidate the cache entries affected by the removal of
    BARRIERs in relax_delay_slots, i.e. for the instructions down to the
    next BARRIER.
    
            PR rtl-optimization/94119
            * resource.h (clear_hashed_info_until_next_barrier): Declare.
            * resource.c (clear_hashed_info_until_next_barrier): New function.
            * reorg.c (add_to_delay_list): Fix formatting.
            (relax_delay_slots): Call clear_hashed_info_until_next_barrier on
            the next instruction after removing a BARRIER.

Diff:
---
 gcc/ChangeLog  |  9 +++++++++
 gcc/reorg.c    | 26 +++++++++++++++++++-------
 gcc/resource.c | 21 ++++++++++++++++++++-
 gcc/resource.h |  1 +
 4 files changed, 49 insertions(+), 8 deletions(-)

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 7b573c07abc..61982897e11 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2019-03-13  Eric Botcazou  <ebotcazou@adacore.com>
+
+	PR rtl-optimization/94119
+	* resource.h (clear_hashed_info_until_next_barrier): Declare.
+	* resource.c (clear_hashed_info_until_next_barrier): New function.
+	* reorg.c (add_to_delay_list): Fix formatting.
+	(relax_delay_slots): Call clear_hashed_info_until_next_barrier on
+	the next instruction after removing a BARRIER.
+
 2019-03-13  Eric Botcazou  <ebotcazou@adacore.com>
 
 	PR middle-end/92071
diff --git a/gcc/reorg.c b/gcc/reorg.c
index dfd7494bf79..84beb9395aa 100644
--- a/gcc/reorg.c
+++ b/gcc/reorg.c
@@ -575,8 +575,9 @@ add_to_delay_list (rtx_insn *insn, vec<rtx_insn *> *delay_list)
 {
   /* If INSN has its block number recorded, clear it since we may
      be moving the insn to a new block.  */
-      clear_hashed_info_for_insn (insn);
-      delay_list->safe_push (insn);
+  clear_hashed_info_for_insn (insn);
+
+  delay_list->safe_push (insn);
 }
 \f
 /* Delete INSN from the delay slot of the insn that it is in, which may
@@ -3211,7 +3212,14 @@ relax_delay_slots (rtx_insn *first)
 
 	      if (invert_jump (jump_insn, label, 1))
 		{
-		  delete_related_insns (next);
+		  rtx_insn *from = delete_related_insns (next);
+
+		  /* We have just removed a BARRIER, which means that the block
+		     number of the next insns has effectively been changed (see
+		     find_basic_block in resource.c), so clear it.  */
+		  if (from)
+		    clear_hashed_info_until_next_barrier (from);
+
 		  next = jump_insn;
 		}
 
@@ -3484,18 +3492,22 @@ relax_delay_slots (rtx_insn *first)
 
 	      if (invert_jump (delay_jump_insn, label, 1))
 		{
-		  int i;
-
 		  /* Must update the INSN_FROM_TARGET_P bits now that
 		     the branch is reversed, so that mark_target_live_regs
 		     will handle the delay slot insn correctly.  */
-		  for (i = 1; i < XVECLEN (PATTERN (insn), 0); i++)
+		  for (int i = 1; i < XVECLEN (PATTERN (insn), 0); i++)
 		    {
 		      rtx slot = XVECEXP (PATTERN (insn), 0, i);
 		      INSN_FROM_TARGET_P (slot) = ! INSN_FROM_TARGET_P (slot);
 		    }
 
-		  delete_related_insns (next);
+		  /* We have just removed a BARRIER, which means that the block
+		     number of the next insns has effectively been changed (see
+		     find_basic_block in resource.c), so clear it.  */
+		  rtx_insn *from = delete_related_insns (next);
+		  if (from)
+		    clear_hashed_info_until_next_barrier (from);
+
 		  next = insn;
 		}
 
diff --git a/gcc/resource.c b/gcc/resource.c
index d26217c056b..32faa73fd5f 100644
--- a/gcc/resource.c
+++ b/gcc/resource.c
@@ -1282,7 +1282,26 @@ clear_hashed_info_for_insn (rtx_insn *insn)
 	tinfo->block = -1;
     }
 }
-\f
+
+/* Clear any hashed information that we have stored for instructions
+   between INSN and the next BARRIER that follow a JUMP or a LABEL.  */
+
+void
+clear_hashed_info_until_next_barrier (rtx_insn *insn)
+{
+  while (insn && !BARRIER_P (insn))
+    {
+      if (JUMP_P (insn) || LABEL_P (insn))
+	{
+	  rtx_insn *next = next_active_insn (insn);
+	  if (next)
+	    clear_hashed_info_for_insn (next);
+	}
+
+      insn = next_nonnote_insn (insn);
+    }
+}
+
 /* Increment the tick count for the basic block that contains INSN.  */
 
 void
diff --git a/gcc/resource.h b/gcc/resource.h
index e3edb242703..c4f8aa20141 100644
--- a/gcc/resource.h
+++ b/gcc/resource.h
@@ -46,6 +46,7 @@ extern void mark_set_resources (rtx, struct resources *, int,
 				enum mark_resource_type);
 extern void mark_referenced_resources (rtx, struct resources *, bool);
 extern void clear_hashed_info_for_insn (rtx_insn *);
+extern void clear_hashed_info_until_next_barrier (rtx_insn *);
 extern void incr_ticks_for_insn (rtx_insn *);
 extern void mark_end_of_function_resources (rtx, bool);
 extern void init_resource_info (rtx_insn *);